In a small bowl, combine the smoked paprika, garlic powder, onion powder, sea salt, and black pepper to create a dry rub.
Rub the spice mixture evenly over all sides of the pork shoulder, pressing it into the meat to ensure it adheres.
Place the seasoned pork into the slow cooker and pour the apple cider vinegar and water around the base of the meat.
Cover and cook on low for 7-8 hours or on high for 4-5 hours until the pork is tender and easily pulls apart with a fork.
While the pork is cooking, prepare the slaw by tossing the shredded cabbage with the yellow mustard and an extra splash of vinegar if desired.
Once the pork is finished, remove it from the slow cooker and discard the excess cooking liquid.
Shred the pork using two forks, then toss the meat with the sugar-free BBQ sauce until well coated.
Lightly toast the whole wheat bun in a dry pan or toaster until golden brown.
Assemble the sandwich by piling the shredded pork onto the bottom bun, topping it with the crisp cabbage slaw, and closing with the top bun.